The inventive concept relates generally to semiconductor memory devices, and more particularly to memory systems comprising nonvolatile memory devices and related read methods.
Semiconductor memory devices can be roughly divided into two categories according to whether they retain stored data when disconnected from power. These categories include volatile memory devices, which lose stored data when disconnected from power, and nonvolatile memory devices, which retain stored data when disconnected from power. Examples of volatile memory devices include static random access memory (SRAM) and dynamic random access memory (DRAM). Examples of nonvolatile memory devices include read only memory (ROM), electrically erasable programmable ROM (EEPROM), phase change random access memory (PRAM), and magnetoresistive random access memory (MRAM).
Flash memory, with is a type of EEPROM, is an especially common form of nonvolatile semiconductor memory device. Due to attractive features such as relatively high storage capacity and operating speed, flash memory devices have been employed in a wide range of applications, such as personal computers (PCs), cellular phones, personal digital assistants (PDAs), digital cameras, camcorders, voice recorders, personal media players, and gaming consoles, to name but a few.
In an attempt to improve the storage capacity and performance of flash memory devices, researchers have developed three dimensional (3D) versions of flash memory in which arrays of memory cells are stacked on top of each other. The development of 3D flash memory devices, however, poses new technical challenges that can potentially diminish device reliability or other characteristics. Accordingly, researchers are actively engaged in the development of new techniques to improve performance, reliability, and other aspects of 3D flash memory devices and other forms of nonvolatile memory.